1. Field of the Invention
The present invention relates to optical probes and optical methods, some embodiments thereof being particularly related to optical probes and methods having utility in the examination of material, especially material in the interior of cavities having restricted access through orifices or passageways, and some embodiments thereof being particularly related to optical probes and methods having utility in the examination of the epithelia and other tissues of anatomical structures within the body cavities and tubular organs and viscera of mammals.
2. Description of Related Art
Various apparatus are known for optically probing the interior of cavities of living and non-living bodies. An early inspection apparatus that uses a disposable sheath and which has particular application to the human cervix is described in U.S. Pat. No. 3,945,371 entitled "Apparatus for Inspection and Sampling in Restricted Aperture Cavities Employing Fibre Optics," issued Mar. 23, 1976 to Adelman. The disposable sheath has an upper duct terminating in a protective window for containing either one fiber optic bundle or two fiber optic bundles used in illuminating tissue and collecting a reflected image from the tissue. The light source is a lamp mounted in a reflector that concentrates the light on the end of the fiber optic bundle being used for illumination. By selecting the numerical aperture, or NA, of the fiber materials used in the image collecting fiber optics bundle, different capabilities are achieved. Fiber materials having an NA of 0.56 permit close inspection of the tissues at a viewing distance of 3 mm with low illumination, while fiber materials having an NA of 0.099 permit a general vantage at a viewing distance of 2 cm with high illumination. The possibility of using lenses is mentioned but not elaborated on.
More recently, an optical probe for use in the diagnosis of the tissues of the human cervix using fluorescence and Raman spectroscopies has been described in U.S. Pat. No. 5,697,373 entitled "Optical Method and Apparatus for the Diagnosis of Cervical Precancers using Raman and Fluorescence Spectroscopies," issued Dec. 16, 1997 to Richards-Kortum et al. The probe, which includes 2 excitation fibers and 5 collection fibers, is a type know as "multi-point contact" because it uses discrete collection fibers disposed a substantially fixed distance from the tissue surface to detect fluorescence and/or Raman emissions from tissue regions proximate the distal fiber ends. The fixed distance is maintained by a quartz shield or window which contacts the tissue under investigation. The probe is part of a diagnostic or screening system that includes electromagnetic sources for generating the excitation energy, filters or spectrum analyzers for isolating wavelengths of interest, and computers for processing the wavelengths of interest to determine the tissue properties of interest. Another optical probe using a large number of paired excitation/collection fibers and a shaped contact window is described in U.S. Pat. No. 5,699,795 entitled "Optical Probe for the Detection of Cervical Neoplasia Using Fluorescence Spectroscopy and Apparatus Incorporating Same," issued Dec. 23, 1997 to Richards-Kortum et al. One embodiment uses 31 fiber optic pairs in a bundle while another embodiment uses 357 fiber optic pairs in a bundle.
One disadvantage of the multi-point contact probe is its shallow depth of field, which generally necessitates that the ends of the collection fibers in the distal end of the probe be positioned a short fixed distance from the target. If any portion of the distal end of the contact probe were not properly positioned, the light energy returning from the target would not be accurately detected due to the critical depth-of-field properties of such a probe. Improper positioning of a contact probe can result from operator error or from a target that is angled with respect to the contact probe's distal end to such an extent that full contact cannot be achieved. Another disadvantage of the multi-point contact probe is its limited resolution, which is a practical result of the difficulty and expense of assembling a large number of very fine fibers into a small probe. Yet another disadvantage of the multi-point contact probe is the lack of uniform excitation and collection of emissions due to the necessary spacing-apart of the excitation fibers and the collection fibers at the distal end of the probe.
Optical devices using lenses avoid some of the disadvantages of point contact optical probes in that they typically have better depth-of-field and better resolution. However, achieving uniform light illumination has remained problematic. Many endoscopes have offset illuminating and observing optical systems and suffer uneven illumination produced by the parallax inherent in the offset arrangement. Some endoscopes have coaxially arranged illuminating and observing optical systems to eliminate the non-uniformity introduced by parallax. For example, European Patent Specification number 0 343 558 B1, published Oct. 12, 1994 and entitled "Image Picking-Up and Processing Apparatus" describes an endoscope having an optical fiber bundle arranged such that its end surface surrounds an objective lens used to detect reflected light. However, the illumination achieved by this ring of discrete optical fibers is not uniform. Another type of endoscope described in U.S. Pat. No. 4,671,630 entitled "Illuminating Optical System for Endoscopes," which issued Jun. 9, 1987 to Takahashi, also has coaxially arranged illuminating and observing optical systems to eliminate the nonuniform illumination introduced by parallax. To overcome the non-uniformity of earlier coaxially-arranged illuminating and observing optical systems, Takahashi uses a rectangular parallelopipedal transparent body or prism in front of the objective lens of the observing optical system and introduces light from the side of the prism. Except where the illumination enters, the sides of the prism are reflecting surfaces. Illumination light introduced into the prism is totally reflected on the objective surface due to the difference in the refractive indices of the prism and air and is also totally reflected by the reflecting side surfaces of the prism, but projects out of the object surface due to the higher refractive index of water relative to air in the tissue against which the prism is pressed during normal use. The object surface is thereby directionally illuminated, nearly obliquely so, which exaggerates shadows from irregularities in the tissue and permits a strong stereoscopic image to be achieved. While this type of illumination may be useful for observation by reflected light, its usefulness for observations based on light interactions with tissue other than reflectance is not described. Another type of endoscope described in U.S. Pat. No. 5,700,236 entitled "Endoscope Attachment for Changing Angle of View," which issued Dec. 23, 1997 to Sauer et al., uses a sheath having a distal portion that contains structure for changing the angle of view and/or illumination angle of an endoscope. Structure for changing the view angle include a prism, and structure for changing the illumination angle include a prism, a curved light guide, and an angled optical fiber. However, the illumination achieved by the discrete optical fibers is not uniform for typical light interaction analysis. No measures are described for achieving uniform light using the alternative techniques.